We study the geological formation and evolution of Late Archean black shales and banded iron formation in the Carajás Mineral Province, Brazil. The project is in cooperation with Vale, and is focussed on the Serra Sul high-grade iron ore deposit, the largest and richest undeveloped iron ore deposit on Earth (measured resources: 9Gt @ 67 % Fe). We combine the study of detailed mineralogy and geochemistry with data from a number of isotope systems (Re-Os. Sm-Nd, O, Mo, Fe, S).